Variable-speed electric motor.



No. 660,908. Patented Oct. 30, I900 B. G. LAMME.

VARIABLE SPEED ELECTRIC MOTOR.

(Application filed June 5, 1899.)

(No Model.)

W/TNESSES /NVENTOH ATTORNEY] m5 NGRMS PETERS co. PHOTO-LITHD"WA5HJNGTON. n. c

UNITED STATES PATENT OFFIc-n.

BENJAMIN G. LAMME, OF PITTSBURG, PENNSYLVANIA, ASSIGNOR TO THEWESTINGHOUSE ELECTRIC AND MANUFACTURING COMPANY,

OF PENNSYLVANIA.

VARIABLE-SPEED ELECTRIC MOTOR.

SPECIFICATION forming part of Letters Patent No. 660,908, dated October30, 1900.

Application filed June 5, 1899. Serial No. 719,428. (No model.)

Be it known that I, BENJAMIN G. LAMME, a

citizen of the United States, residing at Pittsburg, in the county ofAllegheny and State of Pennsylvania, have invented a new and usefulImprovement in Variable-Speed Electric Motors, (Case No. 835,) of whichthe following is a specification.

My invention relates to electric motors, and particularly to machines ofthis general class which are designed and constructed for operation bydirect currents.

The object of my invention is to provide a motor which may be operatedeconomically at widely varying speeds without depending wholly or evenmainly upon variation in the field-magnet excitation of the motor. Inorder to accomplish this result, I propose to provide a motor with anarmature having two windings and two comm utators, the lengths of thetwo windings having approximately the ratio of forty to one hundred, andby means of suitable switching devices to connect the two windings inseries for one rate of speed, to cut the shorter of the two windings outof circuit fora higher speed, to connect the windings in opposition fora still higher rate, and to cut the longer winding out of circuit formaximum speed, it being assumed that the electromotive force supplied tothe armature remains substantially constant. I have found by computationand experiment that the ratio of forty to one hundred in the lengths ofthe two armature-windings insures an increase and decrease in speedbysubstantially equal steps, or as nearly equal as it is possible tosecure by changing the relation and connection of the windings incircuit in the manner described. Of course this ratio need not be exact;but a variation of a comparatively few turns either way, so that theratio is thirtyfive to one hundred or forty-five to one hundred, forexample, serves to make the steps widely unequal. If a more gradualvariation in speed than that which is possible of attainment by themeans described is desired, the field-magnet excitation may be variedbetween the steps described by means of a fieldrheostat, as is usual inthe art.

In the accompanying drawings, Figure 1 is a diagram of a motor and itssupply-circuits and controlling devices embodying my invention, and Fig.2 is a diagram illustrating a portion of the windings of themotor-armature.

The motor 1 has a field-magnet 2, provided with any desired or suitablenumber of poles, the exciting-coils 3 for such magnet being in thisinstance connected across a circuit a 5, supplied by a direct-currentgenerator 6. An adjustable rheostat7is provided in order that a greateror less amount of its resistance may be included in the field-magnetcircuit for the purpose of regulation when desired. The armature 8 ofthe motor is provided with two separate windings, the lengths of whichare in substantially the ratio of forty to one hundred. These windingsare respectively connected to commutators 9 and 10, preferably locatedat opposite ends of the motor. The windings may be constructed andarranged in any suitable manner, provided they are so located as to beproperly subjected to the magnetic field.

In Fig. 2 I have shown one coil 11 of two turns and a coil 12 of fiveturns as indicative of a form of winding suitable for my invention.These coils may conveniently be located in the same slots in thearmature-core, the conductors at each side of each coil being eitherlocated side by side or superimposed. In the case of the coil having thegreater number of turns it will probably be preferable to superpose theconductors occupying the same slot, they being shown in the drawings asside by side merely forconvenience and clearness of illustration. Asufficient number of coils like each of those shown will be employed tocomplete the winding suitable for the size and character of the machine,as will be readily understood.

As a means for making the desired changes in the relation of the twowindings I have shown in Fig. 1 two double-throw switches 13 and let. Onone side of the switch 13 are three pairs of stationarycoutact-termiuals 15, with which codperate the three blades 16, 1'7, and18 pertaining to the movable member of the switch. On the other side ofthis switch are located two pairs of stationary contactterminals inposition to be engaged, respectively, by blades 16 and 18. The switch 1%is also provided with three pairs of stationary contact-tenniuals at oneside and two pairs of such terminals 21 at the other side and with amovable member having three blades 20, 20", and 20 to engage theterminals 20 and two blades 21 and 21" to engage terminals 21. iNhen theblades 16, 17, and 18 of switch 13 are in engagement with the stationarycontact-terminals 15, indicated in the drawings, the twoarmature-windings are connected in series. It now this switch be thrown,so as to bring the blades 16 and 18 into engagement with the stationaryterminals 1!), the shorter armattire-winding will be cut out of circuit.If this switch be opened and the switch 4be thrown to bringthe blades20, 20 and 20 into engagement with the stationary contact terminals 20,the two armaturewindings will be connected in opposition for the nexthigher rate of speed. It the switch be thrown in the opposite directionto bring the blades 21 and2l into engagement with thecontact-terminals21, thelongerarmaturewinding will be cut out ofcircuit. A more gradual change in speed may be effected by moving theswitch-arm of the rheostat 7 before throwing, either of the switches tomake any one of the changes described, so as to bring the speed of themotor, by variation of its field-magnet excitation, to substantially thevalue represented by the armature-circuit connections which it isdesired to make by means of the switch.

While I have illustrated and described a two-circuit.- armature, I donot intend to restrict. myinvention to any specific numberot' suchcircuits. A greater number 0? circuits than two would, however, probablybe too expensive and cumbersome to be desirable in practice, and hence Ihave not deemed it necessary or advisable to set forth specifically amotor and switching devices adapted for more than two armaturecircuits.

I claim as my invention 1. The method of varying-the speed of adirect-current motor provided with a plurality of armature windings ofdifferent lengths which consists in changing the relation and number ofsaid windings in circuit and varying the exciting-current for themotor-field prior to each change in said windings.

2. The method of gradually varying the speed of a direct-current motorprovided with two armattire-windings of diti'erent lengths whichconsists in connecting said windings in series for one rate of speed,gradually reducing the exciting-current for the motorfield, cutting theshorter windings out of circuit, making a further reduction of theexciting-current for the motorfield, connecting the windings inopposition, again reducing the exciting-current, and finally cutting thelonger winding out of circuit.

In testimony whereof I have hereunto subscribed my name this 3d day ofJune, 1899.

BENJ. G. LAMME.

IVitnesses:

WESLEY G. CARR, H. C. TENER.

